The present invention relates to a condenser and, more particularly, to a condenser suitable for use as a condenser in a nuclear power plant, a thermal power plant or a chemical plant.
For example, a steam condenser installed in a nuclear power plant or a thermal power plant is provided with a water chamber at the opposite ends of cooling tubes, and a steam inlet formed so that steam flows perpendicularly to the cooling tubes. Since the tube nest of a general steam condenser has 1,000 to 10,000 cooling tubes, the pressure loss due to the drag of the cooling tubes against the flow of steam is a significant problem in causing steam flow into the interior of the tube nest.
On the other hand, steam contains noncondensable gases, such as air, and the noncondensable gases collect in a low-pressure region of the tube nest as steam condenses into water. The noncondensable gases stagnating within the tube nest tend to cover the surfaces of the cooling tubes and to impede the condensation of the steam. Accordingly, the effective removal of the noncondensable gases is also a significant problem.
Pressure loss caused by the tube nest and the noncondensable gas stagnating region are dependent on the steam flow, which in turn is greatly dependent on the shape of the cross section of the tube nest perpendicular to the cooling tubes. Tube respectively having various shapes have been proposed in an effort to alleviate the problems.
A tube nest of a first prior art arrangement, as disclosed in Japanese Patent Laid-Open No. Sho 61-114087 (1986), U.S. Pat. No. 1,704,484 and DE No. 7,539,721, has flow passages formed in the outer circumference thereof to reduce pressure loss, and an air passage area through which noncondensable gases are guided to an extracting tube or an extracting opening (hereinafter referred to as an "extracting region").
Although these tube nests differ from each other in shape, each of the cooling tubes of those tube nests are arranged in layers of a fixed thickness around the air passage area based on the following common concept. That is, when the cooling tubes are arranged in layers perpendicular to the direction of uniform flow of inflowing steam, steam flows one-dimensionally and condenses on the surface of the layer, and noncondensable gases are guided to the extracting tube by the air passage area formed behind the back side of the layer. Since the surface area of the tube nest is limited by the width of the steam inlet and pressure loss increases, the shape is deformed two-dimensionally without changing the thickness of the layer.
A tube nest of a second prior art arrangement, as disclosed in Japanese Patent Laid-Open No. Hei 4-244589 (1992), has a shape having a plurality of flow passages formed in a layer and having a width decreasing in an arithmetical progression to collect noncondensable gases in a low-pressure region.
A tube nest of a third prior art arrangement, as in Japanese Patent Laid-Open No. Hei 2-242088 (1990), has a layer divided into a plurality of dividual tube nests by flow passages, and the sectional area of one flow passage is varied to collect noncondensable gases in a low-pressure region.
In the first prior art arrangement, noncondensable gases do not necessarily collect in the air passage area behind the layer when the shape of the tube nest is deformed two-dimensionally, and the air passage area does not function effectively when the noncondensable gas stagnates in a region separated from the extracting region. Further, since the velocity of the steam flow in the tube nest having the air passage area is low, the air passage area does not reduce the pressure loss effectively.
In the second and third prior art arrangements, flow passages are necessary to collect the noncondensable gases in the low-pressure region. But since the cooling tubes cannot be disposed in the flow passages, these prior art arrangements are not suitable for a compact steam condenser. Since the different steam passes have different noncondensable gas concentrations, the noncondensable gases mix in the low-pressure region and the stagnating region of the noncondensable gas cannot be reduced to a satisfactory extent. Furthermore, the second prior art has difficulty in collecting noncondensable gases in the direction of the flow passages when the length of the flow passages is long. The third prior art arrangement needs additional equipment because it needs spaces for providing extracting systems respectively with the individual tube nests. Those problems in the prior art are attributable to the shape of the tube nest designed on the basis of the one-dimensional theory.